(1) Field of the Invention
This invention relates to package for electronic devices, in particular to a surface mount package.
(2) Background of the Invention
Many kinds of electronic devices such as capacitors, resistors have long leads. With the advent of printed circuits, it is desirable to use surface mount packages for the devices for easy connection to the printed circuit board.
FIG. 1A shows top view of a conventional package for a typical long lead device. A substrate 20 has two via holes 24 through which the leads of a device (not shown) can extend. FIG. 1B shows the side view of section Axe2x80x94Axe2x80x2 of FIG. 1A. The substrate 20 has two grooves 22 outside the via holes 24. When the leads of a device is inserted through the via holes, the leads are bent outward against the grooves 22 and recessed in the grooves 22 as shown in FIG. 1C. FIG. 1D shows the side view of the package with a device 10 inserted through the package. The two leads 12 of the device 10 are inserted through the substrate 20 and bent outward. Because of the recessed grooves 22, the bottom ends of the bent leads 12 are flush with the bottom of the substrate 20. Thus the bottom surface of the package is flat for surface mounting to a printed circuit board.
However the rounded ends of the leads do not provide a big contact area for soldering to the printed circuit board, the soldering reliability. Although the ends of the leads 12 may be crimped flat to increase the contact area, the increase in soldering area is limited.
An object of this invention is provide a package for surface mounting of long-lead electronic devices. Another object of this invention is to provide a big-area bonding pad for improving the soldering reliability of a surface mount package.
These objects are achieved by using plated through via holes in the substrate of the surface-mount package. The leads of the device are inserted into the plated through via holes. The bottom of the plated through metal is enlarged as a pad to provide a large reliable surface mounting surface. Upon heating the leads are soldered to the walls of the plated through holes. Alternatively, the leads of leads can be folded before inserting into the plated through holes.